How to access the BindingContext of custom control in Xamarin.Forms - xamarin.forms

Question

I have a CollectionView with ItemsSource set to ObservableCollection of type Employee.
The ItemTemplate of the CollectionView is a CustomControl that has 1 BindableProperty of Type Employee
MainPage.xaml:
<CollectionView ItemsSource="{Binding Employees}"
SelectedItem="{Binding SelectedEmployee}">
<CollectionView.ItemTemplate>
<DataTemplate>
<controls:CustomControl Employee="{Binding .}" />
</DataTemplate>
</CollectionView.ItemTemplate>
</CollectionView>
The CustomControl has an image (checked image to indicate selection).
CustomControl.xaml:
<Frame HasShadow="True"
BackgroundColor="Blue">
<StackLayout Orientation="Horizontal">
<Label Text="{Binding Name}" />
<Image Source="check.png" />
</StackLayout>
</Frame>
CustomControl.xaml.cs:
public partial class CustomControl : ContentView
{
public CustomControl()
{
InitializeComponent();
}
public static BindableProperty EmployeeProperty = BindableProperty.Create(
propertyName: nameof(Employee),
returnType: typeof(Employee),
declaringType: typeof(CustomControl),
defaultValue: default(Employee),
defaultBindingMode: BindingMode.OneWay);
public Employee Employee
{
get
{
return (Employee)GetValue(EmployeeProperty);
}
set
{
SetValue(EmployeeProperty, value);
}
}
}
Model (Employee):
public class Employee: INotifyPropertyChanged
{
private int name;
public int Name
{
get
{
return name;
}
set
{
name = value;
OnPropertyChanged(nameof(Name));
}
}
private int isSelected;
public int IsSelected
{
get
{
return isSelected;
}
set
{
isSelected = value;
OnPropertyChanged(nameof(IsSelected));
}
}
#region PropertyChanged
public void OnPropertyChanged(string propertyName)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
public event PropertyChangedEventHandler PropertyChanged;
#endregion
}
I am trying to create simple animation (FadeIn/FadeOut) for the checked image in the CustomControl so when an item is selected the image will fade in, and when unselected it will fade out. I could use IsVisible and set it to true/false but that's ugly.
My idea was to listen to PropertyChanged event of the Employee (which supposed to be the context of my CustomControl), and when the property IsSelected is modified, I will start the animation to show/hide the image. something like this
public CustomControl()
{
InitializeComponent();
(this.BindingContext as Employee).PropertyChanged += CustomControl_PropertyChanged;
}
private void CustomControl_PropertyChanged(object sender, System.ComponentModel.PropertyChangedEventArgs e)
{
if (e.PropertyName == nameof(Employee.IsSelected))
{
//do animation to show/hide image
}
}
But couldn't access the Context of my CustomControl!
When I declare the binding in MainPage.xaml I am passing a single Emplyee objet as BindingContext (that dot, right?):
<controls:CustomControl Employee="{Binding .}" />
but after the CustomControl is initializd, the BindingContext is still null!
public CustomControl()
{
InitializeComponent();
var context = this.BindingContext; //this is null
}
How can I observe the changes on the IsSelected property of the Employee object from my CustomControl?

Answer 1

In your custom control override the OnBindingContextChanged method, inside of that method you should be able to access the binding context that is set for your view.
Ex:
protected override void OnBindingContextChanged()
{
base.OnBindingContextChanged();
var context = this.BindingContext as Employee
}